A Simple Common-Mode Voltage Reduction Method Based on Zero-Sequence Voltage Injection for a Back-to-Back Three-Level NPC Converter

Abstract

This paper introduces a common-mode voltage reduction method based on zero-sequence voltage injection for a back-to-back three-level NPC converter. A detailed analysis in the following paper will show that the amplitude of common-mode voltage in this converter is related to the rising and falling edges of six-phase output voltage pulses, and it is reflected by pulse widths of output voltages in the waveform. When the pulse widths of six-phase output voltages meet a certain relationship, the common-mode voltage will output a higher amplitude. By injecting zero-sequence voltage, widths of output voltage pulses can be changed. According to this principle, a dual-side zerosequence voltage injection method is proposed to change output voltage pulse widths and decrease the common-mode voltage amplitude. Simulation and experimental results show that the proposed method is effective, it can reduce the common-mode voltage to 1/6 of the DC-link voltage in the back-to-back three-level NPC converter.